As the rules say for walkers :"You may play a movement bonus card even if you will not be able to land on a survivor during your turn. The movement bonus will also be lost on traveling through the sewers."

As I understand it, you can use a bonus card to reach a sewer, but all movement that lead you past the sewer will be lost when you will get out of any another sewer, right ?

What happens now if I get into a sewer (without using any card), get out of any another sewer of the map and a survivor is 2 spaces away from my sewer. Can I use a movement bonus card after travelling through the sewers to get to him and attack him ?

My guess is yes, but we were not sure on our last game, so I didnt do it...